Hormonal and autacoid control of cardiac function

This chapter provides an overview of our current knowledge of humoral regulation of fish heart function. The influence exerted by classic cardiac hormones (i.e., catecholamines, angiotensin II, and natriuretic peptides), and the more recently discovered chromogranin A-derived fragments, are discussed. The role of local, i.e., autacoid modulators (the gasotransmitters carbon monoxide, hydrogen sulfide, and nitric oxide), is also summarized. Endocrine and autacoid signaling represent extrinsic and intrinsic regulatory networks, respectively, that are fundamental for preserving cardiac function under developmental and environmental challenges, the latter often extreme. Thus, the evolution of these two humoral systems has allowed for significant variation, and flexibility, in the cardiac function of fishes.By presenting the most recent data, we will highlight the complexity of some mechanisms involved in the functional modulation of the fish heart under both normal and stress-induced conditions. Although there are many gaps in our knowledge due to the variable information available from different fish groups, our aim is to discuss both classic works and recent advances made by our group and by others. In providing this information, we hope to describe, in a spatiotemporal dimension, the mechanisms involved in the integrated control of the fish heart. The chapter will also emphasize the power of the fish heart as an experimental model for identifying humoral-dependent protective mechanisms that are difficult to explore using more conventional mammalian models and experimental approaches.